How to disable in flutter stepper the first cancel button

Question

I currently have a stepper that also works perfectly, but I have the question how to disable the back button at the first step, but in the others it should be displayed.

I modified the stepper with the controlsBuilder but i didnt found a solution where i can disable the back button.

Thanks in advance

Here is a small code snippet from my stepper (not fully):

 controlsBuilder: (BuildContext context,
                    {VoidCallback onStepContinue, VoidCallback onStepCancel}) {
                  return Row(
                    children: <Widget>[
                      FlatButton(
                        onPressed: onStepContinue,
                        child: const Text('Weiter',
                            style: TextStyle(color: Colors.white)),
                        color: Colors.blue,
                      ),
                      new Padding(
                        padding: new EdgeInsets.all(10),
                      ),
                      FlatButton(
                        onPressed: onStepCancel,
                        child: const Text(
                          'Zurück',
                          style: TextStyle(color: Colors.white),
                        ),
                        color: Colors.blue,
                      ),
                    ],
                  );
                },



List<Step> steps = [
      Step(
        title: const Text('TEST'),
        isActive: true,
        state: StepState.complete,
        content: Column(children: <Widget>[
          RadioListTile(
            value: 1,
            groupValue: selectedRadioTile,
            title: Text("XX"),
            onChanged: (val) {
              setSelectedRadioTile(val);
            },
            activeColor: Colors.blue,
            selected: true,
          ),
          RadioListTile(
            value: 2,
            groupValue: selectedRadioTile,
            title: Text("XX"),
            onChanged: (val) {
              setSelectedRadioTile(val);
            },
            activeColor: Colors.blue,
            selected: false,
          ),
        ]),
      ),```

Answer 1

If I understand correctly you want to disable the "Cancel" button conditionally.

You will somehow need to know whether it is the first screen or not. Let's say you have that in a variable called isFirstScreen that you pass to your controlsBuilder method. Then you can disable the button with a ternary operator on the onPressed handler like this:

FlatButton(
  onPressed: isFirstScreen ? null : onStepCancel, // <-- important part
  child: const Text(
    'Zurück',
    style: TextStyle(color: Colors.white),
  ),
  color: Colors.blue,
),

From the Flutter FlatButton docs:

If the onPressed callback is null, then the button will be disabled, will not react to touch, and will be colored as specified by the disabledColor property instead of the color property.